The Raman spectrum of monolayer (ML) MoS2 is remarkably affected by the interaction with metals. In this work, we studied ML-MoS2 supported by the Ag(111) and Ag(110) surfaces by using a combined experimental and theoretical approach. The MoS2 layer was directly grown on atomically clean Ag(111) and Ag(110) surfaces by pulsed laser deposition, followed by in situ thermal annealing under ultrahigh vacuum conditions. The morphology and structure of the two systems were characterized in situ by scanning tunneling microscopy, providing atomic-scale information on the relation between the MoS2 lattice and the underlying surface. Raman spectroscopy revealed differences between the two MoS2-metal interfaces, especially concerning the behavior of the out-of-plane A 1 ' vibrational mode, which splits into two contributions on Ag(110). The metal-induced effects on MoS2 vibrational modes are further evidenced by transferring MoS2 onto a more inert substrate (SiO2/Si), where the MoS2 Raman response displays a more "freestanding-like" behavior. The experimental data were interpreted with the support of ab initio calculations of the vibrational modes, which provided insight into the effect of interface properties, such as strain and out-of-plane distortion. Our results highlight the influence of the interaction with metals on MoS2 vibrational properties and show the high sensitivity of MoS2 Raman modes to the surface structure of the supporting metal.

Two-dimensional (2D) hybrid sp-sp2 carbon systems are an appealing subject for science and technology. For these materials, topology and structure significantly affect electronic and vibrational properties. We investigate here by periodic density-functional theory (DFT) calculations the Raman and IR spectra of 2D carbon crystals belonging to the family of graphdiynes (GDYs) and having different structures and topologies. By joining DFT calculations with symmetry analysis, we assign the IR and Raman modes in the spectra of all the investigated systems. On this basis, we discuss how the modulation of the Raman and IR active bands depends on the different interactions between sp and sp2 domains. The symmetry-based classification allows identifying the marker bands sensitive to the different peculiar topologies. These results show the effectiveness of vibrational spectroscopy for the characterization of new nanostructures, deepening the knowledge of the subtle interactions that take place in these 2D materials.

Graphdiynes (GDYs) as two-dimensional carbon structures based on sp2 hybridized aromatic rings connected by sp-hybridized acetylenic linear links are gathering an increasing popularity, both for their peculiar properties and for the promising applications. In these materials, structural features affect the degree of pi-electron conjugation resulting in different electronic, optical and vibrational properties. In particular, how topology, connectivity between sp and sp2 domains and system size are related with the final properties is fundamental to understand structure-property relationships and to tailor the properties by proper structure design. By using a computational approach based on density functional theory calculations, we here investigate structure-property relations in a class of 1D and 2D GDY molecular fragments as building block models of extended structures. By analysing how the structure can modulate the pi-electron conjugation in these systems, HOMO-LUMO gap is found to depend on the peculiar topology and connections between linear sp domains and aromatic units. A topological indicator is computed, showing a trend with the gap and with the frequency of the main vibrational mode occurring in Raman spectra. Our findings can contribute to guide the molecular design of new GDY-based sp-sp2 carbon materials, aiming at tuning their properties by precise control of the structure.

Much of the communication and scientific dissemination is pedagogically ineffective, even that apparently most successful. Names like Hawking, Penrose and, more recently, Rovelli have achieved extraordinary public success. There have been many Science Festivals and Researcher's Nights. However, serious statistical surveys show that the increased level of scientific literacy produces contradictory and paradoxical effects. What really is missing is the capacity for critical thinking. The problem is not only scientific, sociological and psychological but also ethical. Many popularizers do not tell the truth or they do not say it all. When this happens, communication, conveying a distorted image of science, can become harmful. To remedy is not only important for science, it is important for democracy.

Initially, the theory of propagation of long-wavelength acoustic phonons and Brillouin scattering of laser light in condensed matter is concisely summarized. Then, the case of two relevant classes of complex materials in which Brillouin scattering can be measured is reviewed. First, in low-density, low-dimensional, disordered materials, the crossover between confinement and propagation is discussed on the basis of experimental findings. Moreover, the possibility of measuring the local mechanical properties of these materials at the mesoscale by Brillouin scattering is critically discussed. Second the application of Brillouin scattering to biological materials, a rather hot topic, is presented.

Understanding the electronic structure of metal oxide semiconductors is crucial to their numerous technological applications, such as photoelectrochemical water splitting and solar cells. The needed experimental and theoretical knowledge goes beyond that of pristine bulk crystals, and must include the effects of surfaces and interfaces, as well as those due to the presence of intrinsic defects (e.g. oxygen vacancies), or dopants for band engineering. In this review, we present an account of the recent efforts in predicting and understanding the optoelectronic properties of oxides using ab initio theoretical methods. In particular, we discuss the performance of recently developed dielectric-dependent hybrid functionals, providing a comparison against the results of many-body GW calculations, including G0W0 as well as more refined approaches, such as quasiparticle self-consistent GW. We summarize results in the recent literature for the band gap, the band level alignment at surfaces, and optical transition energies in defective oxides, including wide gap oxide semiconductors and transition metal oxides. Correlated transition metal oxides are also discussed. For each method, we describe successes and drawbacks, emphasizing the challenges faced by the development of improved theoretical approaches. The theoretical section is preceded by a critical overview of the main experimental techniques needed to characterize the optoelectronic properties of semiconductors, including absorption and reflection spectroscopy, photoemission, and scanning tunneling spectroscopy (STS).

Micron-thick boron films have been deposited by Pulsed Laser Deposition in vacuum on several substrates at room temperature. The use of high energy pulses (> 700 mJ) results in the deposition of smooth coatings with low oxygen uptake even at base pressures of 10− 4–10− 3 Pa. A detailed structural analysis, by X-Ray Diffraction and Raman, allowed to assess the amorphous nature of the deposited films as well as to determine the base pressure that prevents boron oxide formation. In addition the crystallization dynamics has been characterized showing that film crystallinity already improves at relatively low temperatures (800 °C). Elastic properties of the boron films have been determined by Brillouin Spectroscopy. Finally, micro-hardness tests have been used to explore cohesion and hardness of B films deposited on aluminum, silicon and alumina. The reported deposition strategy allows the growth of reliable boron coatings paving the way for their use in many technology fields.

Laser interaction with uniform and nanostructured near-critical plasmas has been investigated by means of 2D particle-in-cell simulations. The effect of a nanostructure (modeled as a collection of solid-density nanospheres) on energy absorption and radiative losses has been assessed in a wide range of laser intensities (normalized amplitude a 0 = 1 − 135) and average densities of the target (electron density n e = 1 − 9n c , where n c is the critical electron density). The nanostructure was found to affect mainly the conversion efficiency of laser energy into ion kinetic energy and radiative losses for the highest simulated intensities.

Tungsten trioxide (WO3) is a paradigmatic electrochromic material, whose peculiar optical properties in the presence of oxygen vacancies or intercalated alkali atoms have been observed and investigated for a long time. In this paper we propose a rationalization of experiments based on first principles calculations of optical and electrical properties of oxygen-deficient (reduced) WO3. Our approach is based on a parameter-free dielectric-dependent hybrid density functional methodology, used in combination with the charge transition levels formalism, for studying excitation mechanisms in the presence of defects. Our results indicate that oxygen vacancies lead to a different physics in gamma-monoclinic WO3, depending on the orientation of the W-O-W chain where the vacancy is created, thus evidencing strong anisotropic effects rooted in the peculiar structural properties of the original nondefective monoclinic cell. Different types of oxygen vacancies can hence be classified on the basis of the calculated ground state properties, electronic structure, and excitation/emission energies, giving a satisfactory explanation to a range of experimental observations made on oxygen-deficient WO3.

Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition technique. In situ scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed to characterize morphological, structural and electronic properties of 2D ZnO at the nanoscale. Starting from a sub-monolayer coverage, we investigated the growth of ZnO, identifying different atomic layers (up to the fifth). At low coverage, we observed single- and bi-layer nanocrystals, characterized by a surface moiré pattern that is associated to a graphene-like ZnO structure. By increasing the coverage, we revealed a morphological change starting from the fourth layer, which was attributed to a transition toward a bulk-like structure. Investigation of the electronic properties revealed the semiconducting character of 2D ZnO. We observed a dependence of the density of states (DOS) and, in particular, of the conduction band (CB) on the ZnO thickness, with a decreasing of the CB onset energy for increasing thickness. The CB DOS of 2D ZnO shows a step-like behaviour which may be interpreted as due to a 2D quantum confinement effect in ZnO atomic layers.

We investigated the growth of titanium oxide two-dimensional nanostructures on Au(111), produced by Ti evaporation and post-deposition oxidation. Scanning tunneling microscopy and spectroscopy (STM and STS) and low-energy electron diffraction measurements characterized the morphological, structural and electronic properties of the observed structures. Five distinct TiOx phases were identified: the honeycomb and pinwheel phases appear as monolayer films wetting the gold surface, while nanocrystallites of the triangular, row and needle phases grow mainly over the honeycomb or pinwheel layers. Density Functional Theory investigation of the honeycomb structure supports a (2 x 2) structural model based on a Ti-O bilayer having Ti2O3 stoichiometry. The pinwheel phase was observed to evolve, for increasing coverage, from single triangular crystallites to a well-ordered film forming a (4 root 7 x 4 root 7) R19.1 degrees superstructure, which can be interpreted within a moire-like model. Structural characteristics of the other three phases were disclosed from the analysis of high-resolution STM measurements. STS measurements revealed a partial metallization of honeycomb and pinwheel and a semiconducting character of row and triangular phases.

We investigate band gaps, equilibrium structures, and phase stabilities of several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO2,ZrO2, and WO3. We are particularly concerned with assessing the performance of hybrid functionals built with the fraction of Hartree-Fock exact exchange obtained from the computed electronic dielectric constant of the material. We provide comparison with more standard density-functional theory and GW methods. We finally analyze the chemical reduction of TiO2 into Ti2O3, involving a change in oxide stoichiometry. We show that the dielectric-dependent hybrid functional is generally good at reproducing both ground-state (lattice constants, phase stability sequences, and reaction energies) and excited-state (photoemission gaps) properties within a single, fully ab initio framework.

We investigate the long-standing problem of the hole localization at the Al impurity in quartz SiO$_2$, using a relatively recent DFT hybrid-functional method in which the exchange fraction is obtained \\emph{ab initio}, based on an analogy with the static many-body COHSEX approximation to the electron self-energy. As the amount of the admixed exact exchange in hybrid functionals has been shown to be determinant for properly capturing the hole localization, this problem constitutes a prototypical benchmark for the accuracy of the method, allowing one to assess to what extent self-interaction effects are avoided. We obtain good results in terms of description of the charge localization and structural distortion around the Al center, improving with respect to the more popular B3LYP hybrid-functional approach. We also discuss the accuracy of computed hyperfine parameters, by comparison with previous calculations based on other self-interaction-free methods, as well as experimental values. We discuss and rationalize the limitations of our approach in computing defect-related excitation energies in low-dielectric-constant insulators.

The library of Istituto Lombardo owns two volumes of XVI century (cinquecentine) including physical sections. La nova scientia by Niccolò Tartaglia printed In Venetia: per Nicolò de Bascarini a istantia de l’Autore, 1550 and the De rerum varietate by Girolamo Cardano printed Basileae: per Sebastianum Henricpetri, 1581. Together with the De Subtilitate by Girolamo Cardano, these books contain the general laws of dynamics and, in great detail, a description of the trajectory of a projectile fired from a firearm. Though the general principles are still of Aristotelian derivation, a new attention to experimental facts together with an unconvential pragmatic use of etherogeneous explanation arguments, justified by an essentially practical goal of predictive nature, induce one to identify both Tartaglia and Cardano as true precursors of modern ballistics. Furthermore, the way Cardano revisits the role of driving force played by the projectile-air interaction, following a modified idea of Aristotle due to the lacking of an inertia law in his mechanics, and the concomitant need that air produces also a resisting force, reminds us that, so far, a rigorous microscopic derivation of the exclusively dissipative nature of this force has not been achieved yet as well as a rigorous microscopic derivation of the second principle of thermodynamics.

We investigate the behavior of oxygen vacancies in three different metal-oxide semiconductors (rutile and anatase TiO2, monoclinic WO3, and tetragonal ZrO2) using a recently proposed hybrid density-functional method in which the fraction of exact exchange is material-dependent but obtained ab initio in a self-consistent scheme. In particular, we calculate charge-transition levels relative to the oxygen-vacancy defect and compare computed optical and thermal excitation/emission energies with the available experimental results, shedding light on the underlying excitation mechanisms and related materials properties. We find that this novel approach is able to reproduce not only ground-state properties and band structures of perfect bulk oxide materials but also provides results consistent with the optical and electrical behavior observed in the corresponding substoichiometric defective systems.

We investigate the long-standing problem of hole localization at the Al impurity in quartz SiO2, using a relatively recent DFT hybrid-functional method in which the exchange fraction is obtained ab initio, based on an analogy with the static many-body COHSEX approximation to the electron self-energy. As the amount of the admixed exact exchange in hybrid functionals has been shown to be determinant for properly capturing the hole localization, this problem constitutes a prototypical benchmark for the accuracy of the method, allowing one to assess to what extent self-interaction effects are avoided. We obtain good results in terms of description of the charge localization and structural distortion around the Al center, improving with respect to the more popular B3LYP hybrid-functional approach. We also discuss the accuracy of computed hyperfine parameters, by comparison with previous calculations based on other self-interaction-free methods, as well as experimental values. We discuss and rationalize the limitations of our approach in computing defect-related excitation energies in low-dielectric-constant insulators.

In this work, we describe self-assembled surfaces with a peculiar multiscale organization, from the nanoscale to the microscale, exhibiting the Cassie-Baxter wetting regime with extremely low water adhesion: floating drops regime with roll-off angles < 5°. These surfaces comprise bundles of hierarchical, quasi-one-dimensional (1D) TiO2 nanostructures functionalized with a fluorinated molecule (PFNA). While the hierarchical nanostructures are the result of a gas-phase self-assembly process, their bundles are the result of the capillary forces acting between them when the PFNA solvent evaporates. Nanometric features are found to influence the hydrophobic behavior of the surface, which is enhanced by the micrometric structures up to the achievement of the superhydrophobic Cassie-Baxter state (contact angle (CA) ≫ 150°). Thanks to their high total and diffuse transmittance and their self-cleaning properties, these surfaces could be interesting for several applications such as smart windows and photovoltaics where light management and surface cleanliness play a crucial role. Moreover, the multiscale analysis performed in this work contributes to the understanding of the basic mechanisms behind extreme wetting behaviors.

We report on the synthesis of nanostructured Ag4O4 by thermal evaporation of silver films followed by oxidation with beams of oxygen ions with different kinetic energy in the 50-300eV range. This method, which combines simplicity and versatility, allows to control the oxide structural properties, and in particular to obtain Ag4O4 thin films characterized by different nanoscale morphologies and crystalline structure, depending on the pristine silver layer morphology and on the energy of the oxygen ions. Monoclinic and tetragonal Ag4O4 phases, or a mixture of the two, can be obtained. The nanoscale porosity of the material makes it interesting for applications where surface mediated Ag ion release plays a crucial role. (c) 2012 Elsevier B.V. All rights reserved.

We numerically study light scattering and absorption in self-similar aggregates of dielectric nanoparticles, as generated by simulated ballistic deposition upon a surface starting from a single seed particle. The resulting structure exhibits a complex treelike shape, intended to mimic the morphologic properties of building blocks of real nanostructured thin films produced by means of fine controlled physical deposition processes employed in nanotechnology. The relationship of scattering and absorption cross sections to morphology is investigated within a computational scheme which thoroughly takes into account both multiple scattering and near-field effects. Numerical results are compared with a preexisting single-scattering limited analytical treatment of light scattering in fractal aggregates of small dielectric particles.